1. Field of the Invention
The invention relates to high speed print head systems and methods, and more particularly to print head systems which form high resolution characters from a plurality of individually printed dots with minimum overlap.
2. Description of the Prior Art
Various high speed print head systems have been utilized to provide "printouts" from computer systems or computer controlled systems. A common type of high speed printer, referred to as a dot matrix printer, includes a column of axially movable print rods or wires which are axially movable to provide an impact dot printing function in a so-called dot matrix. All of the commonly known alphanumeric characters and various other symbols can be formed by a system utilizing a 5.times.7, 7.times.9 or other dot matrix configurations. The resolution of standard dot matrix characters printed by means of known dot matrix printers is reltively low. However, it is frequently desirable to print higher resolution characters with dot matrix printers.
One type of dot matrix printing system utilizes 7 or 9 spaced, vertically aligned axially movable print rods which are moved by means of electromagnetic clapper assemblies which controllably strike one end of each of the print rods, causing their opposite ends to impact ribbon and paper supported by a platen. The print head is rigidly supported on a carriage which continuously moves across the paper. By printing both from left to right and right to left, high printing speeds are achieved, although the resolution of resulting printed characters achieved is low. If increased resolution of the printed characters is required, multiple passes of the print head are required for each line of print, wherein for each pass the print head carriage position is offset by predetermined amounts in the X direction and the paper position is incremented by predetermined amounts in the Y direction. However, incrementing of the print head carriage position and incrementing of the vertical paper position are ordinarily achieved by means of stepper motors. Consequently, the smallest increments by which the print head and paper position can be varied have fixed values. Consequently, the amount of dot overlap in both the X and Y directions can not be precisely controlled. In order to obtain a desired level of resolution of characters, a larger amount of dot overlap between adjacently printed dots is required than would be required if the amount of the dot overlap could be precisely controlled. The greater the amount of unnecessary dot overlapping that occurs, the greater the number of individual dot printing operations will be required to print characters having a predetermined level of resolution; therefore, the greater the number of passes of the print head per line of print will be required.
Accordingly, it is an object of the invention to provide a high speed print head system and method which is capable of increasing the speed at which high resolution dot matrix characters can be printed.
Another object of the invention is to provide a print head system and method which reduces the number of passes which a dot matrix print head must make over a particular paper area to print a high resolution character.
Yet another object of the invention is to provide a print head system and method which minimizes the amount of dot overlap resulting from repeated dot printing operations in a particular area to obtain a character having a predetermined resolution level.
An important factor tending to reduce the printing speed of many known dot matrix printers is the fact that the inertia of the print head carriage and the paper advancing mechanism must be overcome for each incremental movement of the print head and paper advancing mechanisms. In addition to reducing printing speed, the overcoming of such inertia requires that high rates of acceleration and deceleration of mechanical parts occur, necessitating the use of expensive high precision, power consuming components.
Accordingly, it is another object of the invention to provide a low cost, high speed print head system and method which eliminates the necessity of stopping of the print head carriage while a particular dot is being printed.
It is a further object of the invention to provide a print head system and method wherein printed dot location is continuously variable in both the vertical and horizontal directions on the paper whereon the dots are to be printed.
A novelty search directed to the present invention uncovered the following U.S. Pat. Nos.: 3,726,379, 3,742,846, 3,884,148, 4,031,992, 4,082,035, and 4,101,017. None of the above patents disclose a print head system for generating a dot matrix wherein the print head position is continuously controllable in both the X and Y directions during high speed printing operations.
It is a yet further object of the invention to provide a high speed print head system and method which produces high resolution character printing by means of dot matrix print rods at high speed and lower cost than print head systems of the known prior art.
A still further object of the invention is to provide a high speed print head system and method which reduces stress and wear on moving mechanical components thereof.
Another object of the invention is to provide a print head system and method capable of greater accuracy in positioning of printed dots than has been previously achieveable with high speed dot matrix printers of the prior art.
Still another object of the invention is to provide a print head system which avoids the need to accurately control vertical movement of paper to achieve increased resolution by making multiple passes of a print head.